Tens of thousands of desperately needed new homes will be created in London under plans to let developers turn office blocks into flats.

Government officials believe that up to 40,000 flats could be created in London and the South-East in a rush to put under-used commercial space to better use. In total, England could get more than 100,000 homes.

Ministers are to announce that developers will be allowed to convert the blocks without seeking permission from councils in a move that property experts said would have a “profound impact” on London.

Property experts said the change in planning rules could unleash a flood of applications to turn hundreds of disused or part-empty commercial buildings into flats that could help ease the capital’s housing crisis. Vacancy rates in commercial buildings are three times higher than in the residential sector.

Adam Pyrke, head of London planning for property adviser Colliers International, said: “There are hundreds of office buildings — mostly small scale — all over London that are suitable for conversion and could add a lot of residential. Each one would probably only provide a handful of units but it is incremental. The planning system has failed to provide enough housing.”

But the Mayor’s chief of staff Sir Edward Lister said Boris Johnson would be “extremely concerned” about any loss of office space in the “City fringes”.

He said: “It’s cheap land and any wholesale conversion to residential could be disastrous for Tech City. We wouldn’t want anything that affected the viability of that.”

Mr Pyrke said he estimated that in central London alone there is three million square feet of vacant space that could be turned into homes.

In the suburbs there were many long-disused offices such as the former Barnet council offices next to Totteridge Underground station that would be “ideal for conversion”. A spokesman for the Communities and Local Government department said: “This Government is committed to getting brownfield land and empty buildings back into productive use. We are currently looking to make it easier to convert empty and under-used commercial space into residential use. ”

But the planned reforms are likely to be resisted by a number of London boroughs, including Kensington & Chelsea, Camden, Hackney, Lambeth and Southwark that all have policies resisting loss of office space. The City is also strongly opposed to large-scale conversion of offices to homes.

Dominic Grace, Savills London head of residential development, said: “Kensington & Chelsea has been concerned about a loss of vibrancy — if too much retail and commercial is lost a place quickly gets a dormitory feel to it.”

Jeremy Raj, property partner at London law firm Wedlake Bell, said: “The Government needs to encourage the biggest shift in housing provision for generations.

“However, it is vital that we do not simply create enclaves for the wealthy.”